In large fluid flow systems, a main valve is typically disposed directly in the fluid line with the valve member being movable between an opened and closed position to meter flow across the valve. Although there are a variety of such main flow valves utilized in the valve art, one particular type typically used in large industrial and commercial applications, includes an elastomeric valve liner disposed transversely across the fluid flow path. This liner rolls back and forth over a plurality of radial slots formed in the valve body in response to variances in loading pressure applied to the opposite side of the liner thereby permitting monitored flow across the valve. Such a valve is disclosed in patent application Ser. No. 730,962, filed Oct. 8, 1976 by Dwight N. Johnson, and is marketed under the registered trademark "ROLL SEAL" by J H INDUSTRIES, Santa Ana, Calif.
In operation, such main flow valves, as well as other valves having similar loading pressure requirements, are regulated or controlled by a pilot valve which may be preset to operate the main flow valve in response to pressure changes sensed by the pilot valve at a desired location within the fluid system. Typically, the monitored pressure (i.e. the measured variable) in the fluid system is directed against a central piston or diaphragm of the pilot valve in opposition to a preset force such as a spring. For pressure reducing applications, the diaphragm or piston carries a valve member which travels to an open position when the monitored pressure acting upon the diaphragm falls below the preset force of the spring. This opening of the pilot valve vents the loading pressure applied to the liner of the main flow valve, thereby causing the main flow valve to open. The valving action of the main flow valve is usually progressive in nature such that as the pilot valve opens further, the main flow valve additionally opens further. Conversely as the pilot valve gradually closes, the main flow valve correspondingly closes in a proportional amount.
Although such prior art pilot valves have proven useful, they have been subject to inherent deficiencies which detract from their overall operation. The prior art pilot valves tend to be unstable during operation which often yields chattering, and there is undesirable phase lag between the sensing of pressure changes within the flow system and the response time in repositioning of the main valve, which often results in rather large variations in monitored system pressure.
In an attempt to eliminate the chattering deficiency associated in the prior art, many prior art pilot valve designs have included external means such as restrictor orifices and friction restrainers to dampen the operation of the pilot valve. However, such orifices and restrainers often become clogged by particulate matter carried within the main flow stream which prevents proper valve operation and, in severe instances, causes complete restrictor blockage.
Similarly, although the prior art pilot valve designs have recognized the undesirable phase lag between the sensing of pressure deviations in the regulated or monitored flow and the corresponding change in the loading pressure, attempts to correct the problem while maintaining valve stability have heretofore been unsuccessful. As a result, undesirably large variations in the regulated pressure within the main fluid system, which adversely affect the overall fluid system operation, are common in the prior art pilot valve fluid control systems.
Thus, there exists a present need in the valve art for a pilot valve regulator which may be effectively utilized to control the operation of the main flow valve disposed within the fluid system without producing chatter or yielding undesirable phase lag in operation.